Conventionally, there is a technique proposed for identifying a person and authenticating the personal identification in accordance with a physical characteristic of a human body. A physical characteristic obtained by an image taking device is compared with a physical characteristic that is registered in advance for a personal identification or personal authentication.
Image taking devices can be divided broadly into a contact type in which the device touches the human body and a noncontact type in which the device does not touch the human body. A noncontact type is desired in a place where an indefinite number of people uses an image taking device, from viewpoints of resistance to soiling, a hygienic aspect and psychological inhibition.
For example, when the image taking device is used for a control of entering and leaving a facility, the image taking process should be performed ever time when a person enters or leaves the facility. In this case, a contact type device is often touched by people. Therefore, a glass face for touching with a hand may become dirty so that the image taking process cannot be performed correctly. In addition, the hygienic problem or the psychological inhibition may be caused by touching the dirty face. For this reason, a noncontact type device is desired.
A noncontact type is superior to a contact type also in the case where the image taking device is used in a place with a strict hygienic rule such as a medical institute or a research institute. In addition, needs of noncontact products are increasing recently as a social trend as understood from that various antibacterial goods and hygienic goods have becomes hit goods.
For taking an image of a physical characteristic, a lighting device is used usually so as to obtain a desired image by removing an influence of external light. However, if the subject is away from the device, it is difficult to irradiate uniform light to the subject, resulting in deterioration of image quality. Therefore, it is difficult to realize a noncontact type device.
In order to solve this problem, Japanese unexamined patent publication No. 2002-92616 discloses a technique for adjusting quantity of light of a light source in accordance with an obtained image. However, there is a problem that as it is necessary to keep the light source lighting normally for taking an image, power consumption may increase and process time increase because of plural times of taking images.
An object of the present invention is to solve this problem by providing a noncontact type image taking device that can obtain an image of good image quality.